Few historians have followed the political careers of Hillary and Bill Clinton more closely than William Chafe, Duke emeritus professor of history. As the primary season kicks into high gear, Chafe is pondering one question in particular: Which version of Hillary Clinton is running for the presidency in 2016?

Chafe explores that question in an expanded, updated edition of his book “Hillary and Bill: The Clintons and the Politics of the Personal,” due out this month from Duke University Press. The book examines the intersection between Hillary and Bill’s marriage and their respective political careers. It also describes Hillary’s two very different personas.

On the one hand, Hillary can be a bridge-builder and reformer, Chafe says. He points to her support of education reform in Arkansas, her lifelong advocacy on behalf of women and children and to her time in the Senate, when she formed strong relationships with Republican lawmakers.

But the former Secretary of State can also be an intensely private person who balks at revealing financial information, demonizes her opponents and refuses to take friendly advice from allies, Chafe says. As an example, he points to her decision to use a private email server while serving as Secretary of State and her failure to compromise on health reform in the early 1990s.

“She’s reluctant to let any of her private stuff go public,” Chafe says. “This goes back to her time in the White House.”

Chafe’s interest in writing about the Clintons goes back to the same era, during Bill Clinton’s presidency. In 1998, Chafe was invited to a White House dinner for historians.

By chance, the Monica Lewinsky scandal had broken just two weeks earlier, and the intense public scrutiny that dogged the Clinton presidency had begun. Chafe fully expected the Clintons to be in crisis mode, and to skip the gathering. Instead, both Hillary and Bill attended, Chafe says.

“They not only come, but each one of them individually talks to everybody in the room,” Chafe says. “You saw firsthand the extraordinary ability of these people to compartmentalize.”

Hillary rose to her husband’s defense during the Lewinsky episode, and her actions helped rescue her husband’s presidency, Chafe says.

Now it’s Bill’s turn to help his wife on the campaign trail. And Bill likely will be a significant help, Chafe says -- as long as he doesn’t go on the attack. During Hillary’s previous run for the presidency in 2008, her husband’s critical remarks about Barack Obama were a strike against the Clinton campaign, he notes.

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Similarly, Chafe says that in the upcoming primaries and the Democratic debate on Feb. 11, it’s to Hillary’s advantage to seize the high road.

“The one thing she can’t allow herself to do is to get down in the gutter with Sanders or anyone else,” Chafe says. “When she descends to playing on their turf and becoming adversarial with them she loses her great benefit, which is to be above it all.”

“She’ll probably be the nominee and be a very successful nominee,” Chafe says. “As long as she can continue to keep her cool and try to be consensus-oriented, then she’ll be okay.”